Updated at 4:15 a.m. ET on Nov. 5: ROME -- A 19-year-old American was in critical condition Friday after he was allegedly stabbed while he slept by a fellow student following a night of partying in the Italian capital, officials told NBC News.

The victim, New Jersey-born Fabio Malpeso underwent surgery for stab wounds to his lungs and other parts of his body. Police said Friday that Malpeso was in critical but stable condition in intensive care at a hospital in Rome.

Authorities said the motive for the attack, which happened in an apartment that overlooks Rome's famous Colosseum early Thursday morning, was unclear. However, detectives suspect "drug- and alcohol-related delirium" might be a factor.

The alleged assailant, who was taken to a police station and then a prison in central Rome, was named as Reid Alexander Schepis, 20. The suspect and victim are both students at John Cabot University, an American college in Rome.

Police said Schepis, a resident of Reggio Calabria in southern Italy, appeared to have joint U.S. and Italian citizenship, but they were working to establish his nationalities.

Lawyer: Suspect a 'model student'Schepis' lawyer, Vincenzo Comi, said his client was "distraught and exhausted," after visiting the young man in jail Friday.

"He is clearly under shock, and nothing in his past could have prepared him for this. He has never had any problems with the law and has always been a model student with top grades,” Comi said, adding he did not want to say what Schepis had told him at this stage.

Comi said Schepis’ mother was American and his father Italian, and as far as he was aware Schepis had dual citizenship.

A third man, an Italian aged in his 30s named Andrea Rinaldi, suffered injuries to his arms and hands trying to defend Malpeso, and was also in the hospital, police said.

Paolo Guiso, a judiciary police inspector who is leading the investigation, told NBC News Friday that Schepis and Malpeso had returned to the apartment, where Malpeso's sister Federica and Rinaldi were also staying, after partying in a nightclub Wednesday night and early Thursday.

Yara Nardi / F3 Press

The building where Schepis is alleged to have stabbed Malpeso is not far from the Coliseum in central Rome.

"Federica, Rinaldi and Fabio went to bed at 6 a.m. [Thursday]. Reid stayed in the living room. At a certain point, he went to the kitchen, fetched a knife and went into Fabio's room, where he started to stab the sleeping youth," Guiso alleged.

"Hearing the screaming and commotion, Rinaldi and the victim's sister ran in to see what was happening. They stepped in to defend Fabio, which resulted in Rinaldi suffering cuts to his hands and arms," he said.

"The motive of the attack is still not clear. At present we … believe that the violence was brought on due to a drug- and alcohol-related delirium," Guiso added.

'Best friends'Guiso said early Friday that he had not been able to speak properly with Schepis as he was "still half asleep and at times catatonic ... he was almost in a state of unconsciousness at times."

"We have taken him to Regina Coeli prison in the heart of Rome. Within 48 hours from the arrest, he will have to go before the judge who will need to confirm his arrest," he added.

Marta Canigiulia, 20, a student at John Cabot, told NBC News Friday that she was friends with Schepis and Malpeso, though she had only recently met the latter.

“They were best friends ... they are best friends, I hope they still are,” she added. “I loved them for the fact that they were always very cheery. They would always come up to you and say: ‘Hi Marta, what’s up?’ They were always smiling.”

Referring to Schepis, Canigiulia said with tears in her eyes, “he is a good person.”

“I can’t explain why this happened. Probably it’s because of drugs,” she speculated.

Geraldine Gully, 18, another student, said she did not know Schepis and Malpeso personally but “saw them all the time at school. ... They seemed like very good friends. I was so shocked to hear what had happened because it was so unexpected and you wouldn’t believe it,” she said.

In a statement, John Cabot University President France Pavoncello said he was dealing “with this situation personally” with support from other staff and was in touch with the “involved parties and their families.”

He confirmed the suspect and victim were students at the university, saying they were roommates in an off-campus apartment.

“I trust you will all join me in sending our prayers to the victim's family for their son's full recovery as well as to the family of the alleged attacker, who is likely shattered by this tragic event,” he added.